1. Field of the Invention
The present invention pertains generally to a light source device that utilizes the light emission or heat generated in discharge gases through a dielectric barrier discharge in a dielectric barrier discharge lamp light source device such as a dielectric barrier discharge lamp that generates ultraviolet light rays through an excimer light emission or a noble gas lamp that combines a phosphor.
2. Description of Related Art
U.S. Pat. No. 4,983,881 discloses a dielectric barrier discharge, also known as a ozonizer discharge or a silent discharge, which is utilized as an excimer lamp for ozonizers or dielectric barrier discharge lamps, or, as disclosed in U.S. Pat. No. 5,977,722, the dielectric barrier discharge may also utilized as a noble gas light emission lamp.
A conventional dielectric barrier discharge lamp generally includes two dielectrics and at least one dielectric that is present between two electrodes which enclose a discharge space within the dielectric barrier discharge. In such a connection, a sealed unit combines the dielectrics in the dielectric barrier discharge lamp. Current does not directly flow from the electrodes to the discharge space since the dielectrics are interposed between discharge space and the electrodes. Consequently, current flows through dielectrics functioning as capacitors. Equal charges of opposite signs are evoked by dielectric polarization on the side of each electrode on the discharge space side of each dielectric and, are discharged between the opposing dielectrics that hold discharge space between them. For that reason, a high voltage alternating current of approximately 10 kHz-10 MHz and 1 kV-10 kV is applied to both electrodes when lighting the dielectric barrier discharge lamp. The ideal conditions associated with the voltage, frequency, and alternating current voltage waveform would be selected in accordance with the structure of the dielectric barrier discharge lamp 1, the discharge gas constituents, pressure, etc. Of course, the so-called discharge mode termed high frequency discharge or electric field discharge as well as an intermediate form of discharge between these and dielectric barrier discharge are included therein.
As indicated above, dielectric barrier discharge lamps are extremely useful, however, they do present safety problems because of their need for the application of high voltage. For example, if the output terminals of the power supply device have connectors, there is always the possibility of a poor contact developing, but current would naturally still flow due to discharge if the contact were slightly defective and the lamp would light as though it were apparently normal since the output terminals are high-voltage charging units. Consequently, a poor contact would not immediately be apparent. If such events should actually transpire, localized heating due to abnormal discharge at the defective contact or eventual deterioration of peripheral insulation depending on the ruminant could occur, and could subsequently lead to a fire.
As shown in FIG. 9, a second safety hazard could develop as a result of a crack in the electrodes 5, 6, whereby current would flow due to the discharge at the crack site, and theoretically lead to localized heating. Consequently, the electrodes 5, 6 could both theoretically break if cracks should develop in the sealed unit 2. Furthermore, localized heating due to a surface discharge developing in the gap between the electrodes 5, 6 on the surface of lamp sealed unit 2 is also theoretically possible.
Moreover, localized heating due to the development of dielectric barrier discharge at the insulation borders of cables connected to both electrodes 5, 6 is also theoretically possible. Furthermore, there is always the possibility of poor contact or poor conduction brought about by poor conduction attributable to poor contact with connectors, imperfect soldering or breakage of circuit board soldering even within transformers in the power supply device or in the section from the secondary side output terminal of a transformer to output terminals of the power supply device. However, current would naturally still flow due to discharge if the contact or conduction were slightly defective and the lamp would light as though it were apparently normal. Consequently, a poor contact or poor conduction would not immediately be apparent. If such events should actually transpire, localized heating due to abnormal discharge at the site of defective contact or defective conduction, or eventual deterioration of peripheral insulation depending on the luminant could occur, and that could theoretically lead to a fire.
Such abnormal discharge could be detected using a photodetector for the light emission. In addition, such detectors as a thermal detector, acoustic detector or vibration detector could be used as well. The detection of ozone generated by ultraviolet rays from abnormal discharge basically would be possible using an ozone detector. Even if detection were possible using the photo, thermal, acoustic, vibration, or ozone detectors, it would be unreliable since sites where abnormal discharge could occur are continuously distributed over a broad range, as mentioned above. Furthermore, these safety countermeasures have involved reliance on lowering the probability of abnormal discharge from occurring by using structures and materials having high insulation resistance since the said countermeasures would be extremely uneconomical as well as unreliable.
Accordingly, an object of the invention is to overcome the said difficulties by providing a dielectric barrier discharge lamp light source device capable of safely and economically preventing the hazards of abnormal discharge which could occur within transformers of the power supply device of a dielectric barrier discharge lamp light source device or in the section from the secondary side output terminal of a transformer to the electrodes.
This is achieved by providing a dielectric barrier discharge lamp light source device having a discharge space filled with a discharge gas that emits light through a dielectric barrier discharge. The device is provided with a dielectric barrier discharge lamp having a structure in which dielectrics are interposed between at least one of two electrodes to induce a discharge phenomenon in the discharge gas and a power supply device, and a power supply device having an abnormal discharge detection circuit to detect abnormal discharge occurring within transformers in the power supply device or in the section from the secondary side output terminal of a transformer to the electrodes. The power supply device acts to halt the supply of alternating current high voltage from the power supply device to the dielectric barrier discharge lamp when the abnormal discharge detection circuit detects an abnormal discharge. The abnormal discharge detection circuit has the ability to detect only an abnormal discharge arising from electrical behavior of the power supply device, without detecting a special abnormal discharge due to photo, acoustic, thermal or chemical conditions.
The dielectric barrier discharge lamp light source device includes a power supply device having an output level detection means that detects an output substantially proportional to the voltage provided to the dielectric barrier discharge lamp, a drive circuit that provides high voltage alternating current power to the dielectric barrier discharge lamp, and a capacity control circuit which regulates the capacity of the drive circuit, wherein the drive circuit has the ability to set the power supply capacity through a capacity regulating signal created by the capacity control circuit. The capacity control circuit effects feedback control of the capacity regulating signal so as to minimize the error between the output level detection signal created by the output level detection means and the output level target signal. The abnormal discharge detection circuit can detect at least one of a deviation of the capacity regulating signal from the upper limit of the established capacity, or a deviation of the capacity regulating signal from the lower limit of the established capacity.
Alternatively, the power supply device of the dielectric barrier discharge lamp light source may include an output level detection means which detects an output substantially proportional to the power provided to the dielectric barrier discharge lamp, a drive circuit that provides high voltage alternating current power to the dielectric barrier discharge lamp, and a capacity control circuit that regulates the capacity of the drive circuit, wherein the drive circuit can set the power supply capacity by capacity regulating signal created by the capacity control circuit. The capacity control circuit effects feedback control of the capacity regulating signal so as to minimize the error between output level detection signal created by the output level detection means and output level target signal. The abnormal discharge detection circuit can detect if the frequency range component of a capacity regulating signal having preset fluctuation exceeds a predetermined level.
In another embodiment, the dielectric barrier discharge lamp light source includes a power supply device having a drive circuit that provides high voltage alternating current power to the dielectric barrier discharge lamp, output level detection means which detects the output substantially proportional to the power provided to the dielectric barrier discharge lamp in a stage after the drive circuit. The abnormal discharge detection circuit can detect whether the frequency range component of the output level detection signal created by the output level detection means having preset fluctuation exceeds an predetermined level.